Conventionally, there is a well known lighting apparatus for controlling a plant disease. The above lighting apparatus emits ultraviolet rays which are controlled to include a wavelength component in a UV-B range (the wavelength range 280 to 340 nm) and set a wavelength component in a UV-C range (the wavelength range 100 to 280 nm) to almost zero (refer to Japanese Laid-Open Patent Publication No. 2005-328734, for example). According to the above lighting apparatus, a spore formation and a hyphal growth of filamentous fungi which cause gray mold, powdery mildew, downy mildew, anthracnose, or the like can be inhibited.
There is also a well known lighting apparatus for controlling a plant disease which emits ultraviolet rays, which has a wavelength range 250 to 375 nm, red light, blue light, and yellow light to reduce a disease and insect damage on a plant (refer to Japanese Laid-Open Patent Publication No. 2001-28947, for example).
However, the lighting apparatus described in the Publication No. 2005-328734 cannot emit UV-C to the plant and thereby cannot reliably inhibit the spore formation and the hyphal growth of the filamentous fungi described above. Moreover, almost no visible light is emitted, so that it is difficult to promote a plant growth. There is also a possibility that the plant gets too used to ultraviolet rays due to a continuous irradiation of ultraviolet rays and thereby a generation of an antibacterial substance or resistive substance is reduced, so that the induction of resistance against the plant diseases is often difficult. Moreover, there is also a possibility of a leaf scorch caused by the continuous irradiation of ultraviolet rays.
The lighting apparatus described in the Publication No. 2001-28947 emits ultraviolet rays in the UV-C range as well as ultraviolet rays in the UV-B range and thereby can reliably inhibit the spore formation and the hyphal growth of the filamentous fungi described above. Moreover, the visible light is emitted, so that the plant growth can be promoted, however, as described above, there is a possibility that the induction of resistance against the plant diseases is reduced or the leaf scorch occurs due to the continuous irradiation of ultraviolet rays.